1. Field
The present disclosure relates to positive electrodes for all-solid batteries and all-solid batteries including the positive electrodes, and more specifically to positive electrodes for all-solid batteries having excellent battery characteristics and all-solid batteries including the positive electrodes.
2. Description of the Related Art
Among lithium-ion secondary batteries, all-solid batteries using solid electrolytes are known. An all-solid battery includes an electrolyte layer including a solid electrolyte, electrodes (positive and negative electrodes) formed on opposite sides of the electrolyte layer, and a current collector attached to each electrode. As the solid electrolyte, a sulfide-based, i.e., a sulfide-containing, solid electrolyte having high ion conductivity is known.
For a lithium-ion secondary battery, a carbon material that does not include lithium is used as an active material in a negative electrode and a transition metal oxide including lithium, such as a lithium cobalt oxide (LiCoO2), a lithium nickel oxide (LiNiO2), or a lithium manganese oxide (LiMn2O4) is used as a positive active material. Furthermore, because the positive active material has low lithium-ion conductivity, a solid electrolyte is generally included in the positive electrode.
As a solid electrolyte included in the positive electrode, a sulfide-based solid electrolyte having excellent lithium-ion conductivity is used; however, due to high reactivity of sulfide, the sulfide-based solid electrolyte reacts with the electrode active material, more specifically, with the positive active material, to form a highly resistive layer of an oxide at an interface of the solid electrolyte and the positive active material, and increases interfacial resistance. Thus, a lithium-ion secondary battery formed therefrom does not have good charge and discharge characteristics.
In one method known in the art to solve the above-described problems, a lithium-ion conductive oxide is coated on a surface of a positive active material particle to inhibit counter diffusion between the positive active material and the solid electrolyte, which inhibits the formation of the highly resistive layer on the interface of the positive material and the solid electrolyte, to thereby improve output characteristics of an all-solid lithium secondary battery formed therefrom. Coating the lithium-ion conductive oxide on the surface of the positive active material particle is performed by a method such as electro-spraying; however, processes for the coating can be difficult or complicated and thus, the processes are difficult to use on a commercial scale that would allow production to keep up with the increase in demand for lithium-ion secondary batteries.